This study was undertaken to assess a new method for the non-invasive determination of cerebral blood flow without the use of radioactive tracers. Specifically, we used a new 19F NMR technique to measure the clearance of a fluorinated inert gas, CHF3, from the brain. We tested the new technique by comparing the cerebral blood flow values determined by 19F NMR with cerebral blood flow values determined simultaneously by radioactive microsphere techniques. The cerebral blood flow values determined by 19F NMR and radioactive microsphere techniques agreed reasonably well, and showed the same response to variations in the arterial CO2 level. We conclude that the 19F NMR technique gives a quantitative measure of cerebral blood flow. We used NMR techniques to localize the 19F NMR spectra (and thus the blood flow) to a well defined 4 cc volume in the brain. Using this localization technique, the 19F NMR approach was now non-evasive, and thus applicable to clinical studies. However, there were two drawbacks to this technique. First, the spatial resolution was rather poor, and second, only one region of the brain was investigated at a time. Both these problems were circumvented by a new technique that was developed in the last year. Instead of obtaining spectra from a single localized region, we used NMR techniques to image the cerebral blood flow over the entire brain. The spatial resolution for the imaging studies (0.8 cc) is much better than the spatial resolution obtained with the previous technique (4 cc).